With increasing substrate concentration, the rate eventually levels off as enzymes become saturated.

With increasing substrate concentration, the rate eventually levels off as enzymes become saturated.

• A. It continues to rise indefinitely
• B. It levels off
• C. It drops to zero
• D. It oscillates

Answer: (B)

When substrate concentration increases, the reaction rate rises because more substrate molecules can bind to available enzyme active sites. But as more substrate is added, those active sites become fully occupied and the enzymes are saturated. Once all enzymes are busy, adding more substrate can’t speed up the reaction any further, so the rate levels off at its maximum value (Vmax). This shows the limit is the enzyme’s catalytic capacity, not the amount of substrate. The other ideas don’t fit: the rate wouldn’t keep climbing forever because there are only so many enzyme molecules to work with; it wouldn’t drop to zero simply from more substrate, and it wouldn’t oscillate in a simple enzyme-catalyzed reaction without additional regulatory factors.

When substrate concentration increases, the reaction rate rises because more substrate molecules can bind to available enzyme active sites. But as more substrate is added, those active sites become fully occupied and the enzymes are saturated. Once all enzymes are busy, adding more substrate can’t speed up the reaction any further, so the rate levels off at its maximum value (Vmax). This shows the limit is the enzyme’s catalytic capacity, not the amount of substrate.

The other ideas don’t fit: the rate wouldn’t keep climbing forever because there are only so many enzyme molecules to work with; it wouldn’t drop to zero simply from more substrate, and it wouldn’t oscillate in a simple enzyme-catalyzed reaction without additional regulatory factors.